Method and apparatus for shaping tubes

ABSTRACT

Elongated workpieces are axially positioned in a chamber formed with a cavity that is designed to axially guide a die that is forced through the cavity over the workpiece. In one embodiment a tubular workpiece is shaped by both the die and a mandrel. In another embodiment the die is a deformable die and the cavity tapers so that the die is caused to close over and shape the workpiece during drawing.

United States Patent Hinshaw 1 June 27, 1972 54] METHOD AND APPARATUSFOR 3,327,313 6/1967 Hinshaw ..72/274 x SHAPING TUBES 3,484,806 12/1969Huddleston.. ..72/60 2,372,917 4/1945 Tuttle ...72/60 1 Inventor! JohnHinshaw, Garden Grove, Calif- 3,449,935 6/1969 McAllen ..72/60 73 A e:The Battelle De I ent Co ti 1 sslgne Columbus Ohio ve 0pm wonPrimaryExaminer-Charles W. Lanham Assistant Examiner-Michael J. Keenan[22] Flledi May 19, 1969 Attorney-Gray, Mase & Dunson 211 App]. No.2825,482 [57] I ABSTRACT Elongated workpieces are axially positioned in achamber E (5] formed with acavity that is designed to axially guide adie that is forced through the cavity over the workpiece. In one [58]Field of Search ..72/283, 285, 57, 274, 63 bqdimem a tubular workpieceis shaped y both the die and a mandrel. In another embodiment the die isa deformable die [56] References Cited and the cavity tapers so that thedie is caused to close over and UNITED STATES PATENTS shape theworkpiece during drawing.

Powell ..72/285 16 Claims, 11 Drawing Figures PATENTEDJum x972 SHEET 1OF 5 AI mm 8 PATENTEDJummn 3.672.201 sum aur s PATENTfnJunzv I972 SHEETt Of 5 nova kVv/@%////////////////////%Z%7//// I I I I I l I I I I I I II I I I l I I I i I l I I METHOD AND APPARATUS FOR SHAPING TUBESBACKGROUND This invention relates to improvements in shaping elongatedworkpieces and relates in particular to a new and novel method andapparatus for shaping tubes.

In drawing and sinking elongated workpieces such as bars and tubesconsiderable difficulty is experienced in maintaining accurate alignmentof the draw bench, of the mandrel (where used), and of the die itself.Vibrations ordinarily encountered in manufacturing facilities frequentlycause misalignment. Also, the operation of the drawbench itself maycause such misalignments. Wear of drawbench parts may also throw thebench out of alignment.

Additionally, in my US. Pat. No. 3,327,513 I disclose a method fortapering tubes wherein tubes are drawn into conformity with a taperedmandrel by forcing an expandable die or drawing ring over the tube withthe mandrel inserted therein. Although this procedure is successfullyemployed to produce tapered tubular objects, it does not readily lenditself to mass production techniques. After each tubev is drawn it mustbe individually stripped from the mandrel and a new mandrel-tubeassembly and die mounted to the die holder and retaining plate andaligned for the next drawing operation. Such time consuming proceduresdetract from the attractiveness of the process particularly where it isdesired to turn out quantities of parts.

I have now devised a method and apparatus that make it possible toreproduce drawn tubes with accuracy and precision not heretoforepossible. Further, I find that my invention is particularly adaptable todrawing tapered tubes by the expandable die technique.

My method and apparatus lends itself to modern rapid productionprocedures whether one is sinking, drawing, or tapering workpieces.

In one embodiment of my invention a workpiece is axially formed in achamber that is provided with a piston-shaped die or die holder.

The piston and chamber type of construction is particularly amenable toaccurate alignment. Consequently, by providing an axially aligned dieopening in the piston and by axially positioning a workpiece in thechamber, it is possible to draw or sink the workpiece by driving thepiston axially within the chamber over the workpiece to form theworkpiece with a degree of precision and reproducibility not heretoforeknown Where tube drawing, of course, a mandrel must first be axiallypositioned within the chamber.

In another embodiment of the present invention, the inner chamber or thechamber cavity walls vary tangentially from the axis of the chamber. Inthis embodiment the piston or die is constructed of a deformablematerial such as copper, brass, or an elastomeric material. Theworkpiece is axially positioned in the chamber and the deformable die isforced through the chamber over the workpiece. The cavity wall causes itto close over and form the workpiece in accordance with the tangentiallyvarying cavity wall.

A particularly useful application of this embodiment of my inventionrelates to tapering. For example, a tapered mandrel may be axiallymounted within a chamber formed with inner walls that at leastsubstantially conform in shape to the mandrel so that the spacingbetween the mandrel and the walls of the chamber are substantiallyuniform. The tube is positioned over the mandrel within the chamber anda deformable die is forced through the chamber from the large end of themandrel to the small end. The wall of the chamber forces the die againstthe workpiece and causes it to conform with the mandrel surface thusforming a tapered tube.

This arrangement automatically effects a degree of alignment difficultto attain by my prior procedures and, as will be obvious from thedrawings and accompanying detailed description, lends itself well toautomatic processing procedures.

The invention is best described in conjunction with the drawingswherein:

'FIG. 1 is an elevational view in cross-section showing a chamber with amandrel, die, and workpiece mounted therein and constructed inaccordance with the present invention;

FIG. 2 shows the apparatus of FIG. 1 during drawing;

FIG. 3 is a cross-sectional view of a chamber with a mandrel, tube, anddie mounted therein in conformity with the practice of the presentinvention when tapering tubes;

FIG. 4 is the view of FIG. 3 after drawing;

FIG. 5 is a fragmented cross-sectional view of the apparatus of FIGS. 3and 4 showing a tube being stripped from the mandrel;

FIG. 6 is a cross-sectional view of a chamber that constitutes anotherembodiment of the present invention shown in an open position andshowing the ends of mandrels positioned for automatic insertion into thechamber;

FIG. 7 is a fragmentary perspective view of segment 34 of FIG. 6;

FIG. 8 is a cross-sectional view of the chamber of FIG. 6 shown in itsclosed position and containing the tube and die positioned therein andwith the mandrels positioned for taper- 8;

FIGS. 9 and 10 are cross-sectional views of the apparatus of FIG. 6showing the die and tube in different stages of forming; and

FIG. 11 is a fragmentary cross-sectional view of the end of theapparatus of FIG. 8 showing the tube being stripped from the mandrel.

In FIG. 1 there is shown a cross-sectional view of a cylindrical chamber11 that is similar in construction to a hydraulic cylinder that has beendivided into two parts horizontally (segments 11a and Ilb) and clampedor bolted together as shown at 13. Positioned within cylinder 1 1 is apiston 15 (also shown in cross-section) which may be identical to thatused in hydraulic cylinders in that it is provided with sealing rings17. Chamber 11 is also provided with a hydraulic fluid source 19 and apressure relief outlet 21 which permits one to drive the piston in thedirection of the arrow with hydraulic force.

Piston 15 is also provided with an opening 23 and axially positionedseat 23a designed to receive a drawing die 25.

There is positioned at either end of chamber 11 axially aligned clamps27 that are disposed to receive a mandrel 29.

Mandrel 29 is provided with an extending stem 29a which provides a tuberestraining shoulder 29b.

Operation of the device of FIG. 1 consists of removing segment Ila,positioning the mandrel through the die seat with die 31 and pointedworkpiece 33 positioned thereon, abutting the die seat of piston 15 withthe die, closing and sealing segment 11a, and providing hydraulic orfluid pressure behind piston 15 through conduit or source 19 so thatthecylinder is forced through the chamber and workpiece 33 is drawnovermandrel 29 (see FIG. 2).

With this arrangement, precision drawing can be effected on each stroke.

The various possible modifications of the device of FIG. I will beobvious to those skilled in the art of metal working. Fluids other thanhydraulic (i.e., gas, particulate materials, etc.) can be used. The dieand piston can be integral. Many chamber opening devices can beemployed. Piston 15 can be driven by mechanical forces. When sinkingmandrel 29 is omitted and workpiece 33 is axially anchored to clamps 27(in this event, the workpiece must, of course, be of greater length).The workpiece may be solid metal (bars, rods, etc.

The embodiment of FIGS. 3 to 5'consists of a cylindrical chamber 10formed with a tapering inner surface or cavity 12. Deformable die orring 14 is positioned over the end of the tube 16 that is to be tapered.The die and tube assembly is then positioned within the chamber 10 inthe manner shown, with the die 14 fitting snugly in the enlarged end oftapered inner surface or cavity 12.

Tapered mandrel 18 is mounted axially on the plunger 20 of a hydrauliccylinder (not shown) that is positioned axially in relation to chamber10. When plunger 20 is retracted, the mandrel I8 is completely withdrawnfrom the chamber. When the die 14 and tube 16 are positioned within thechamber 10,

the plunger 20 is extended to position mandrel 18, tube 16, and die 14within chamber 10 in the manner shown by FIG. 3.

The tapered mandrel and cavity are of substantially complementary shapeso that the distance between the mandrel surface and surface 12 issubstantially uniform.

Positioned around plunger 20 is a hollow plunger 22 which may be drivenby a conventional dual ram and yoke arrange ment (not shown) or anymechanical driving means. Hollow plunger 22 extends around the end oftube 16 and bears on the die or ring 14. By exerting sufficient pressureon the back of die 14, the die is forced through the cavity 12 (see FIG.4). Since the cavity tapers, the OD. of the die or ring must shrink asthe die passes through the cavity and accordingly inward pressure fromthe surface 12 forces tube 16 to draw onto the surface of the mandreland forces the die to elongate (see FIG. 4).

Hollow plunger 22 may then be withdrawn and a stripper ring 24positioned in the end thereof. Plunger 20 is then withdrawn to strip thetube from the mandrel (see FIG. The assembly is now prepared forreloading with a die and tube assembly.

In the apparatus of FIGS. 6-11 chamber 30 is formed from twohorizontally disposed segments 32 and 34. Segment 32 is provided withmeans for raising and lowering the segment into meshing engagement withsegment 34 that consists of a vertically disposed plunger 36 that leadsto an appropriately mounted hydraulic cylinder (not shown).

Each segment 32 and 34 is formed with one-half of a venturi-shapedcavity 38 which is completed when the segments are in meshingengagement.

venturi-shaped cavity 38 is not of true venturi configuration in thatone side of the venturi 38a tapers from a slightly larger diameter thanthe other side 38b. The end of each side of venturi cavity 38 terminatesin a nontapering chamber 400 and 40b. Cavity 38 and chambers 40a and 40bare provided with end openings 42a and 42b which are disposed to engageand clamp around the mandrel and tube surfaces in a manner described ingreater detail herebelow.

Openings 42a and 42b are provided with seals 47 to form gas-tight sealsaround the tube and mandrel. Also, seals are provided between segments32 and 34 (see FIG. 7).

Segment 32 is provided with openings 43a and 43b leading to chambers 40aand 40b. Openings 43a and 43b lead to conduits 45a and 45b which in turncommunicate with a gas pressure source and a vacuum source respectively(not shown). Opening 43a is positioned rearwardly in chamber 40a (towardgripper 44a) to leave space for die 64 to be positioned forwardly inrespect to this opening (toward surface 384).

Tube and mandrel grippers 44a and 44b which are shown to be verticallypositionable by plungers 46 that lead to appropriately positionedhydraulic cylinders (not shown) are stationed adjacent either end ofopenings 42a and 42b. Grippers 44a and44b are preferably keyed to theiradjacent segments 32 and 34 for accurate positioning (see FIG. 7).

Spring loaded tube stripping bolts 48 are attached to, positionedaround,'and extend slightly beyond the tube and/or mandrel gripping faceof grippers 44a and 44b (see FIG. 7).

Tapered mandrels 50 and 52 mounted to plungers 54 and 56 which lead toappropriate hydraulic cylinders (not shown) are axially positioned inrespect to chamber 38. Mandrel 52 is provided with a locking pin 58 thatis disposed to engage a receptacle 60 formed in the end of mandrel 50when both plungers are extended to form a venturi-shaped mandrel withinchamber 38. Since the taper of surface 38a is greater than the taper ofsurface 38b, the spacing between mandrel 50 and surface 38a will begreater than the spacing between mandrel 52 and surface 38b. Preferablythe spacing between the mandrels and surfaces 38 will be uniform (thoughdiffering between 380 and 38b).

In operation, segment 36 is raised and grippers 44a and 44b are opened(see FIG. 6). A tubular workpiece 62 of appropriate length having anexpandable die 64 positioned thereon is seated in segment 34 so that oneend is within the jaws of grippers 44a but does not extend beyond thespringloaded bolts 48 (see dotted outline FIG. 6).

The plungers 54 and 56 are then extended, positioning mandrels 50 and 52within tubular workpiece 62.

Plunger 36 is actuated to bring segment 32 into engagement with segment34 and sealing the cavity 38 around workpiece 62 and mandrel 50 andmandrel 52, respectively. Plungers 46 are actuated to cause grippers 44aand 44b to engage tube 62 and mandrel 50 and mandrel 52 respectively(see FIG. 8).

The apparatus is now prepared for forming and die 64 is caused to moveover mandrel 50 and tube 62 by a sudden supply of gaseous pressurewithin chamber 44a behind the die supplied through the conduit 45a andpassageway 43a. Optionally the die may be propelled by a vacuum createdin chamber 40b by being drawn through conduit 45b and opening 43b.Preferably, the force driving die 64 will be a combination of suchdriving forces.

As die 64 progresses over tube 62 and mandrel 50, the die is compressedand deformed by the diminishing area of the space between surfaces 38aand mandrel 50. Thus tube 62 is formed over mandrel 50 (see FIG. 9).Once the die reaches mandrel 52 it commences to expand drawing workpiece62 onto the surface of mandrel 52 (see F IO. 10). Although die 62 is nowexpanding, it will not reassume its original shape due to the fact ithas elongated while on mandrel 50. However, since the distance betweenmandrel 52 and surface 39b is less than the distance between mandrel 50and surface 38a, the die will continue to seal cavity 38 and the gaseouspropelling force will not escape around the die.

When the die reaches chamber 40b and workpiece 62 is formed, plunger 36is retracted slightly to relieve the seal and pressures within cavity 38that may interfere with the removal of the mandrels and/or workpiece.Plungers 46 are retracted a predetermined amount so that grippers 44aand 44b release the mandrels and workpiece, but are positioned so thatspringloaded bolts 48 will engage the edge of workpiece 62. Plungers 54and 56 are then retracted. Spring-loaded bolts 48 engage the leadingedge of workpiece 62 and strip it from the mandrels (see FIG. 11). Die62 is, of course, also stripped from the mandrel 52 by chamber 40b orgrippers 44b. The plunger 36 is then further retracted, formed workpiece62, and used die 62 are removed and the assembly is prepared for anotherworkpiece and die.

It will be appreciated that where the deformable die 64 of the apparatusof FIGS. 6-11 is constructed of a nonelastomeric material such as redbrass, sinking is only partially possible. Sinking is possible only inthat portion of the cavity 38 represented by the surfaces 38a sincemandrel 52 is essential to cause the die to expand and form theworkpiece.

It will be obvious to those skilled in the art that the apparatus ofFIGS. 6-11 is readily adaptable to tapering tubes rather than forming aventuri shape. The die may be propelled through the cavity by any forcemechanical or chemical. For example, explosives may be advantageouslyused to drive the die. Also, cavity 38 may be readily adapted for theuse of mechanical die driving means such as the hollow plunger 22 of thedevice of FIGS. 3-5.

Die 64 will normally be constructed of a deformable metal such as redbrass, however, many materials may be employed as die materials. Forexample, where the tube 62 is constructed of thin wall metal, it may bedesirable to employ a die constructed of an elastomeric resin. In thisinstance it may be desirable to provide identical spacing between wall38b and mandrel 50 since the elastomer will recover from elongation whenpassing over mandrel 52.

In the embodiments of the present invention shown and described abovewhere tubular shapes are drawn over a mandrel, the cross-sectionaldimensions of the workpiece may be reduced, the tubes may be elongated,tapered and/or formed into venturi configurations. It will also beappreciated that as in conventional drawing over a mandrel and through adie wall sizing may be effected either in conjunction with one or moreof the aforementioned forming procedures or as an independent formingstep.

For example, the walls of workpiece 33 of the embodiment of FIG. 1 maybe merely reduced in gage rather than the workpiece being reduced indiameter or the wall gage may be reduced simultaneously with reducingthe diameter of the tube. Obviously where the wall gage is reduced thetube is caused to elongate.

The mandrel 18 of the embodiment of FIGS. 3 and 4 may have a slightlygreater or slightly less taper than the cavity surfaces 12 so that theworkpiece 20 is formed into a tapered tube having an increasing ordecreasing gage from its large diameter to its small diameter. In a likemanner, the spacing between mandrels 50 and 52 and cavity surfaces 38aand 38b may be selected to effect a desired gage or gage variation in aresultant venturi shape (FIGS. 8-10).

The ability to size walls and particularly to vary the gage of taperedtubes by varying the taper of the mandrel and cavity is significant forthe production of tapered golf club shafts, light poles, etc., where theparameters of mechanical strength distribution along the tube dictatethe use of heavier gage metal for greater relative strength in the smalldiameter end of the tube.

For the purposes of the present invention, the term venturi shape shallbe interpreted to apply to the shape of a surface whether the outsidesurface of a solid member or the inside surface of a chamber and shallmean roughly the shape of opposing cones aligned approximately apex toapex which may or may not have a straight or parallel surfaced areaseparating them.

For the purposes of the present invention the term tube shall includeany hollow elongated body such as pipe, conduit, etc. The term shallalso include cross-sectional shapes that are not necessarily round butwhich may be oblong, square, triangular, hexagonal, octagonal, etc. Themandrel, of course, must conform in shape to the tube or elongatedmember being drawn.

I claim:

1. Apparatus for forming an elongated workpiece comprismg:

a. a chamber formed with at least one bearing surface disposed to guidean axially positioned die so that its orifice substantially coincideswith the axis of said chamber when the die is axially forced throughsaid chamber;

b. means for axially mounting said workpiece within said chamber; and ic. means for forcing a die axially through said chamber while in contactwith said bearing surface and over said workpiece so as to form saidworkpiece;

d. wherein the inner walls of said chamber form said bearing surface andthe distances between them vary along the axis of said chamber, and saiddie is a deformable die.

2. The apparatus of claim 1 wherein a mandrel is axially positionedwithin said chamber said mandrel being of substantial complementaryshape in respect to said inner walls so that the distance between themandrel surface and said inner walls is substantially uniform.

3. The apparatus of claim 1 wherein said bearing walls taper from alarge diameter to a small diameter.

4. The apparatus of claim I wherein said bearing walls are ofsubstantial venturi configuration.

5. The apparatus of claim 1 including an axially positioned mandrelhaving substantially complementary shape to said walls.

6. The apparatus of claim 4 including an axially positioned mandrelhaving substantially complementary shape to said walls.

7. The apparatus of claim 2 wherein said mandrel tapers relative to saidinner walls so that the distances between the mandrel surface and saidinner walls vary along the axis of said chamber.

8. The method of forming an elongated workpiece comprising:

a. axially aligning a workpiece in a chamber having at least one bearingsurface disposed to guide a die so that its orifice coincides with theaxis of said chamber; and b. forcing a die axially through said chamberover said workpiece while in contact with said bearing surface so as toform said workpiece;

c. wherein the inner walls of said chamber form said bearing surface andthe distances between them vary along the axis of said chamber, and saiddie is a deformable die.

9. The method of claim 8 including the step of axially positioning amandrel within said chamber that has a substantially complementary shapein respect to said inner walls, positioning a tubular workpiece oversaid mandrel and forming said workpiece by forcing a deformable diethrough said chamber over said workpiece and mandrel.

10. The method of claim 9 wherein said mandrel and inner walls aretapered so that said tubular workpiece is tapered.

11. The method of claim 9 wherein said mandrel and inner walls areventuri shaped so that said tubular workpiece is formed into a venturishape.

12. The method of claim 9 wherein said mandrel tapers relative to saidinner walls so that the distances between the mandrel surface and saidinner walls vary along the axis of said chamber.

13. Apparatus for forming a tubular member comprising:

a. a housing formed with an elongated cavity and axially alignedopenings at either end, the inner walls of said cavity being positionedto guide an axially oriented die through said cavity while maintainingits axial alignment, said housing being divided into two longitudinalsections, each said segment containing an elongated portion of saidcavity so that when said segments are aligned in abutting relationshipsaid cavity is formed;

b. means for separating said segments and bringing said segments intoaligned abutting relationship;

c. means for axially positioning an elongated workpiece in the cavityportion of at least one of said segments so that said workpiece may beso positioned while said segments are separated; and

d. means for forcing an axially oriented die through said cavity oversaid workpiece after said workpiece is positioned and said segments arebrought into abutting relationship;

e. wherein means are provided for positioning a mandrel in said cavityso that a tubular elongated workpiece may be positioned in the cavityportion of said segment and said mandrel may be positioned therein andsaid die may form said tube between said inner cavity wall and saidmandrel; and wherein said cavity is tapered and said mandrel is ofsubstantially complementary shape so that a deformable die will formsaid tubular workpiece into a tapered tube.

14. The apparatus of claim 13 wherein said cavity is venturi shaped andsaid mandrel is of substantially complementary shape so that adeformable die will form said tubular workpiece into a venturi shapewhen forced through said cavity.

15. The apparatus of claim 14 wherein the venturi shape is of slightlygreater diameter where the die is forced to taper downwardly than wherethe die is forced to taper upwardly.

16. The apparatus of claim 15 wherein gripping means are positioned ateither end of said cavity to grip the ends of the tubular workpieces andthe mandrel and seal the cavity and means are provided for creatinggreater fluid pressure in back of said die than in front of said die soas to propel said die through the cavity.

1. Apparatus for forming an elongated workpiece comprising: a. a chamberformed with at least one bearing surface disposed to guide an axiallypositioned die so that its orifice substantially coincides with the axisof said chamber when the die is axially forced through said chamber; b.means for axially mounting said workpiece within said chamber; and c.means for forcing a die axially through said chamber while in contactwith said bearing surface and over said workpiece so as to form saidworkpiece; d. wherein the inner walls of said chamber form said bearingsurface and the distances between them vary along the axis of saidchamber, and said die is a deformable die.
 2. The apparatus of claim 1wherein a mandrel is axially positioned within said chamber said mandrelbeing of substantial complementary shape in respect to said inner wallsso that the distance between the mandrel surface and said inner walls issubstantially uniform.
 3. The apparatus of claim 1 wherein said bearingwalls taper from a large diameter to a small diameter.
 4. The apparatusof claim 1 wherein said bearing walls are of substantial venturiconfiguration.
 5. The apparatus of claim 1 including an axiallypositioned mandrel having substantially complementary shape to saidwalls.
 6. The apparatus of claim 4 including an axially positionedmandrel having substantially complementary shape to said walls.
 7. Theapparatus of claim 2 wherein said mandrel tapers relative to said innerwalls so that the distances between the mandrel surface and said innerwalls vary along the axis of said chamber.
 8. The method of forming anelongated workpiece comprising: a. axially aligning a workpiece in achamber having at least one bearing surface disposed to guide a die sothat its orifice coincides with the axis of said chamber; and b. forcinga die axially through said chamber over said workpiece while in contactwith said bearing surface so as to form said workpiece; c. wherein theinner walls of said chamber form said bearing surface and the distancesbetween them vary along the axis of said chamber, and said die is adeformable die.
 9. The method of claim 8 including the step of axiallypositioning a mandrel within said chamber that has a substantiallycomplementary shape in respect to said inner walls, positioning atubular workpiece over said mandrel and forming said workpiece byforcing a deformable die through said chamber over said workpiece andmandrel.
 10. The method of claim 9 wherein said mandrel and inner wallsare tapered so that said tubular workpiece is tapered.
 11. The method ofclaim 9 wherein said mandrel and inner walls are venturi shaped so thatsaid tubular workpiece is formed into a venturi shape.
 12. The method ofclaim 9 wherein said mandrel tapers relative to said inner walls so thatthe distances between the mandrel surface and said inner walls varyalong the axis of said chamber.
 13. Apparatus for forming a tubularmember comprising: a. a housing formed with an elongated cavity andaxially aligned openings at either end, the inner walls of said cavitybeing positioned to guide an axially oriented die through said cavitywhile maintaining its axial alignment, said housing being divided intotwo longitudinal sections, each said segment containing an elongatedportion of said cavity so that when said segments are aligned inabutting relationship said cavity is formed; b. means for separatingsaid segments and bringing said segments into aligned abuttingrelationship; c. means for axially positioning an elongated workpiece inthe cavity portion of at least one of said segments so that saidworkpiece may be so positioned while said segments are separated; and d.means for forcing an axially oriented die through said cavity over saidworkpiece after said workpiece is positioned and said segments arebrought into abutting relationship; e. wherein means are provided forpositioning a mandrel in said cavity so that a tubular elongatedworkpiece may be positioned in the cavity portion of said segment andsaid mandrel may be positioned therein and said die may form said tubebetween said inner cavity wall and said mandrel; and f. wherein saidcavity is tapered and said mandrel is of substantially complementaryshape so that a deformabLe die will form said tubular workpiece into atapered tube.
 14. The apparatus of claim 13 wherein said cavity isventuri shaped and said mandrel is of substantially complementary shapeso that a deformable die will form said tubular workpiece into a venturishape when forced through said cavity.
 15. The apparatus of claim 14wherein the venturi shape is of slightly greater diameter where the dieis forced to taper downwardly than where the die is forced to taperupwardly.
 16. The apparatus of claim 15 wherein gripping means arepositioned at either end of said cavity to grip the ends of the tubularworkpieces and the mandrel and seal the cavity and means are providedfor creating greater fluid pressure in back of said die than in front ofsaid die so as to propel said die through the cavity.